36o 



MARKETABLE BRITISH MARINE FISHES 



the yolk of the egg or from nutritious secretions of the ovary. The two 

 sources of nourishment often exist together, but generally the more 

 abundant one is, the more diminished is the other, either being capable 

 of supplying the place of the other. We may consider those cases in 

 which the nourishment is derived chiefly from the yolk as being more 

 primitive. Cases of this kind occur among the Cyprinodonts, for 

 instance in the species of Gambusia. 



Gajubiisia patruelis is a species living in the fresh waters of Virginia. 

 The adult males are only \\ inch long, the females if inch. The 

 ventral (so-called anal) fin has the anterior rays elongated to form an 

 intromittent organ, but there is no tube running down these rays. In 

 copulation the male has been observed to have his head turned towards 

 the tail of the female, and to insert the end of the prolonged ventral fin 

 into the opening of the ovary. The ovaries of the two sides are united 



Fig. 158- 



Fig. 159, 



Fig. 158. — Developing Egg of the Viviparous Blenny taken from the ovary Sept. 28th. 

 Magnified 12 times. Fig. 159, Young of the Viviparous Blenny, taken from the 

 ovary of the mother on Nov. 24th ; magnified twice. The circle and straight 

 line show the actual size of the egg and length of the unborn voung fish. (After 

 Rathke.) 



into one, and at each gestation twenty to twenty-five yellowish eggs each 

 about Y2- i^ch in diameter are produced. These eggs do not leave the 

 follicles in which they are formed, but an opening is formed at the 

 •outer part of the follicle ; through this opening sperms enter and fertilise 

 the egg, which goes on developing in the follicle. It is very remarkable 

 that in this case the ovary has lost its tubular or sac-like character, and 

 the germinal tissue is exposed in the general body-cavity, the young 

 escaping at birth by an abdominal pore. Another peculiarity is that 

 the egg does not appear to be provided with an egg-membrane, a struc- 

 ture which is unnecessary in an egg that develops within the follicle in 

 which it is produced. The walls of the follicle are richly supplied with 

 blood-vessels, and by this means the developing fish is provided with 

 oxygen ; but although the follicle contains liquid around the embryo 

 this does not appear to contribute to the nourishment of the latter, for 

 .the yolk is not exhausted until the young fish is completely developed 



